– pick a photo with a motif which fits for a panorama view
– select a cutout of 1500 x 500 pixels and save this photo (Photoshop or so)
– cut this wide photo in 3 equal parts of 500 x 500 pixels
– now you have 3 triple photos
– post the 3 photos in the right order on your photo stream
– make sure, that the layout and the number of other photos shows the triple on one line.